CDMA communication systems are well known in the art. Generally, such systems comprise communication stations which transmit and receive wireless communication signals between each other. Typically, base stations are provided which are capable of conducting wireless concurrent communications with a plurality of subscriber stations. In CDMA systems specified by the Third Generation Partnership Project (3GPP), base stations are called Node Bs, subscriber stations are called User Equipments (UEs) and the wireless interface between the Node Bs and UEs is known as the Uu interface. FIG. 3 illustrates a typical 3GPP CDMA system.
Orthogonal variable spreading factor (OVSF) codes provide an orthogonal code set of variable spreading factors. In the prior art, methods exist for allocating a set of OVSF codes of different data rates employing Walsh codes of variable length. The code assignment is made on the basis of channel data rates in a manner that results in improved utilization of the available frequency spectrum.
An alternative method to obtain OVSF codes based on the code tree structure is based on the modified Hadamard transformation, which requires two indices to indicate a specific code, (i.e., spreading factor and code number). In order to handle the code allocation process, an ASSIGNED list and a BUSY list are conventionally generated.
These prior art methods have drawbacks in that they require a large amount of memory to store a large number of codes, or require fast processing speeds to generate the codes or effectively allocate the available codes.